<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script type="text/javascript">
			var a = prompt("请输入a的值:");
			if(a>60){
				alert("b="+1);
			}else if(a>70){
				alert("b="+2);
			}else if(a>80){
				alert("b="+3)
			}else if(a>90){
				alert("b="+4)
			}
		</script>
	</body>
</html>
